Dual-axial centrifugal flow blower wheel impellers or fans of the squirrel-cage type are of course well-known, and a conventional impeller of this type is exemplified in FIG. 1, the same being generally designated by the reference character 10. The impeller is seen to comprise, for each direction of axial air flow, a bell-shaped, annular hub member 12 co-axially secured to one side of a support plate 14 which is disposed at an axially central location of the impeller 10. The hub members 12 may be secured to support plate 14 by conventional means, such as, for example, rivet-type fasteners 16. Annular plates or end rings 18 are disposed axially fowardly and rearwardly of central support plate 14, and a plurality of axially extending, arcuately-configured blades 20 are fixedly secured between each of the end plates 18 and the central support plate 14 in a peripheral arrangement. The blades 20 may likewise be secured to plates 14 and 18 by rivet fasteners 22.
During use and operation of the impeller 10, the hub members 12 are of course fixedly secured to the drive shaft, not shown, of a driving motor, also not shown, whereby the impeller 10 is caused to rotate, for example, in the direction as depicted by arrow A. As a result of such rotational movement, air flow is axially induced into the impeller 10 from both ends thereof, in opposite directions, and centrifugally discharged in a radially outward manner. This air flow pattern has thus accounted for the nomenclature of these types of fans or impellers as dual-axial-centrifugal flow blower wheels.
Bell-shaped hub members 12 are commonly employed within axial-centrifugal flow blower wheels because of the laminar, nonturbulent air flow patterns efficiently generated during the process of altering the air flow from its axial induction path to its radial discharge path. As can further be appreciated, most of the air flow leaving the hub members 12 and being discharged toward the peripheral blades 20 will encounter the blades at their root ends, that is, the ends of the blades adjacent central support plate 14. While this air flow pattern may ostensibly seem to be innocuous, in fact, it has been observed that when, for example, the impellers 10 are employed as exhaust means for air flows containing abrasive particles, the concentration of the air flow at the root end portions of the blades 20 has deleteriously affected the structural integrity of the impeller blades 20 by causing premature wear of such blade portions. Consequently, the expected service lives of these impellers have been substantially foreshortened.